So that quote is actually taken out of context. The Senator knows that finstas are, and is using it to drive a different argument - that Instagram is incentivized to help teenagers bypass parental control https://www.theverge.com/2021/10/1/22704308/finsta-instagram...

> “Finstas are fake Instagram accounts. Finstas are kids’ secret second accounts. Finstas often are intended to avoid parents’ oversight. Basically, Facebook depends on teens for growth,” Blumenthal said. “Facebook also knows that nearly every teen in the United States has an Instagram account; it can only add more users as fast as there are new 13-year-olds.”